1. Field of the Invention
This invention relates to thermoplastic elastomers.
2. Introduction to the Invention
Thermoplastic elastomers, which are often referred to as TPE's, are well known. The TPE's in general use contain (i) polymeric blocks (usually referred to as "hard" blocks or A blocks) which (a) are amorphous and have a second order transition point, T.sub.gh, which is well above room temperature, or (b) have a crystalline polymer backbone and have a crystalline melting point, T.sub.mh, which is well above room temperature, and (ii) amorphous polymeric blocks (usually referred to as "soft" blocks or B blocks) which have a glass transition point, T.sub.gs, which is well below room temperature. Each soft block is linked to at least two hard blocks, so that at temperatures between T.sub.gs and T.sub.mh, or T.sub.gs and T.sub.gh, the amorphous B blocks are tied together, resulting in elastomeric behavior. Above T.sub.mh or T.sub.gh, melting or softening of the hard blocks permits viscous flow of the polymeric chains, resulting in thermoplastic behavior. Known TPE's are described for example in U.S. Pat. Nos. 4,260,659 (Gobran), 4,361,526 (Allen), 4,483,978 (Manser), 4,551,388 (Schlademan), 4,554,324 (Husman), 4,656,213 (Schladman), 4,764,586 (Manser), 4,778,852 (Futamura), 4,806,613 (Wardle), 4,919,737 (Biddle et al.), 4,952,644 (Wardle et al.), and 4,976,794 (Biddle et al.) and in the articles in Polymer, 29 (7), 1233-1239 (1988) Kallitsis et al.; J. Appl. Poly. Sci 37 (1), 267-281 (1989) Murphy et al.; J. Poly. Sci, Part A, Poly Chem, 28 (9) 2393-2401 (1990) Talukder et al.; Makromol Chem, 190, 1069-1078 (1989) Khan et al., 191, 603-614, 615-624, and 2341-2354 (1990) Fakirov et al., and 191 2355-2365 (1990) Gogeva; and Macromolecules 18 (2), 123-127 (1985) Miyamoto et al., and 23,333-337 (1990) Chow. The disclosure of each of those patents and articles is incorporated herein by reference.
It has also been proposed in the patent literature to use, as components in temperature-sensitive dispensers for pesticides, disinfectants, drugs and other active agents, block copolymers containing a side chain crystallizable (SCC) polymer and a second polymer which exhibits a glass transition or melting point higher than the SCC polymer, such that the entire mass exhibits mechanical stability above the melting point of the SCC polymer but below the transition of the second polymer. See U.S. Pat. No. 4,830,855 (Stewart), the disclosure of which is incorporated herein by reference. The block copolymer undergoes a rapid change in permeability to the active agent in the region of the melting point of the SCC polymer, and the second polymer ensures that the SCC polymer remains immobilized even if its melting point is reached or exceeded.